1. Technical Field
The present invention relates to DNAs encoding proteins participating in fungal cell wall synthesis, proteins encoded by the DNAs, methods for examining whether or not a certain compound has an influence on the transport process involved in the transport of glycosylphosphatidylinositol (GPI)-anchored proteins to the cell wall, and antifungal agents having an influence on the transport process involved in the transport of glycosylphosphatidylinositol (GPI)-anchored proteins to the cell wall.
2. Background Art
In recent years, management of opportunistic infections are gaining importance more than ever due to an increase in the number of elderly people and immunocompromised patients as a result of advanced chemotherapies, etc. Deep-seated mycosis due to Candida, Aspergillus, Cryptococcus, and such, account for a portion of such opportunistic infections, and the proportion is increasing year after year. The fact that opportunistic infections by many avirulent bacteria occur one after another, shows that the problem of infectious diseases will not end as long as there are underlying diseases that diminish the immune functions of patients. Although new strategies for infectious diseases control, including the problem of resistant bacteria, will be one of the crucial issues in the soon-to-come aged society, extremely few effective therapeutic agents exist at present.
Up to now, therapeutic agents for fungal infections were developed based mainly on the strategy of creating novel compounds by chemically modifying known structure. However, due to problems such as the emergence of resistant bacteria, the development of new drugs based on new mechanisms is eagerly anticipated.
Considering such circumstances, the inventors focused on a novel approach in the area of antifungal agents in which the variety of therapeutic agents is still insufficient. Namely, the present inventors concentrated on influencing the onset, progress, and persistence of infections by preventing pathogens from showing pathogenicity. In order to avoid the establishment and progress of infection, the inventors thought that the most effective way would be to inhibit the adhesion onto the host, which is the first step in the establishment of infection, and the subsequent progression of colonization. In addition, a new unprecedented approach, namely, the inhibition of the expression of adhesion factors themselves, was also carried out.
In order to inhibit the expression of adhesion factors, the present inventors directed their attention to the hypothesis that cell wall glycoproteins such as adhesion factors are first GPI (Glycosylphosphatidylinositol)-anchored to the cell membrane, and then transported to the cell wall (FIG. 1). To date, 30 or more cell wall glycoproteins including adhesion ligands have been found to be transported via GPI-anchoring (referred to as GPI-anchored proteins). Hence, it was thought that if this transport step is inhibited, it may be quite possible to inhibit the expression of adhesion factors and major cell wall-constituting proteins at the cell wall (Hamada K et al, Mol. Gen. Genet., 258: 53-59, 1998). GPI-anchored proteins have been reported to be present in Candida, which is a pathogenic fungi (Kapteyn J C et al, Eur. J. Cell Biol., 65:402-407, 1994).
The inventors initiated their research believing that novel antifungal agents that inhibit cell wall synthesis can be produced by inhibiting the process that transports GPI-anchored proteins existing in the cell membrane of a fungus to the cell wall.